The present invention relates to force sensing means, and more particularly to force sensing means for a driving device which employs a shape memory alloy.
A driving system for driving a load is generally constructed of the load, a force trasmission unit and a driving portion, the load being coupled to the driving portion by the force transmission unit. The driving system of this type comprises means to sense a force acting on the driving portion, for such purposes as protection against an overload acting on the driving portion, etc. The sensing is performed with a force sensor such as load cell. In this case, the force sensor needs to be assembled in a part of the force transmission unit. Therefore, the structure of the force transmission unit has been complicated, and it has been difficult to render the driving device small in size and light in weight.
Moreover, the force is detected with a tension, a distortion stress, or the like which acts directly on the force sensor. In case of sensing a great force, therefore, the structural strength of the force sensor itself has needed to be sufficiently high, and the force sensor has tended to become large in size.
On the other hand, as the driving system for driving the load as stated above, there is one employing a shape emory alloy. Examples are disclosed in British Pat. No. 1554738 and No. 1573204. When, in the driving system of this type, it is intended to control a force acting on the driving portion, the installation of a force sensor is necessitated, and the construction of the driving system becomes complicated and large in size, likewise to the foregoing.